We propose to determine the total sequence of several ribosomal cistrons (rrn) of Escherichia coli. Ribosomes play such a central role in gene expression that it is important to understand their structure and function in detail. Thus the importance of this study derives primarily from the necessity of having precise nucleic acid sequence information to evaluate RNA:RNA and RNA:protein interactions within the ribosome. In addition to structure-function considerations, evidence indicates that the rrn cistrons of E. coli are not identical. This heterogeneity may have functional significance. Precise nucleic acid sequence data is required to evaluate any detected heterogeneity. These studies are possible because technology is now available for determining the sequence of large stretches of DNA. The methods which we will use include the newly developed chemical method of Maxam and Gilbert for sequencing specific DNA fragments, and a variety of techniques associated with recombinant DNA technology. These include the cleavage and mapping of DNAs with restriction endonucleases, identification of fragments by RNA/DNA hybridization using the Southern technique, cloning of specific E. coli DNA fragments in vectors such as pBR313 and lambda-Charon phage, and large scale preparation of plasmid DNA and specific restriction fragments. First, we will examine the total DNA sequence of the rrn cistron derived from the transducing phages phi80d3. We will then compare this sequence with other existing sources of rrn cistrons. Comparisons with the phi80d3 rrn will first be made by restriction mapping and then by a more detailed sequence analysis of one other rrn. Finally we will clone and examine rrn cistrons de novo from E. coli DNA. This will increase the variety of ribosomal genes examined and minimize the possibility of accumulating mutants or rearrangemnts in the passively carried ribosomal DNA sequences.